1. Field of the Invention
The present invention relates to an apparatus for observing electronic components, and more particularly to an electronic component observation system for observing outer leads of a semiconductor device in the process of assembling the semiconductor device.
2. Description of the Prior Art
In a conventional semiconductor-device fabrication technique generally known as the "tape automated bonding method", semiconductor chips are bonded in succession to a film carrier of synthetic resin such as polyimide, and after that the film carrier is stamped at predetermined intervals by a punching machine, thereby fabricating semiconductor devices. The semiconductor devices thus fabricated are then bonded to a substrate. The bonding process of this kind is called the "outer lead bonding". In a modern outer lead bonding, a number of very fine outer leads projecting from a semiconductor chip with a very narrow inter-lead space or pitch are aligned with, and then bonded to, a corresponding number of very fine electrodes formed on the substrate with a very fine pitch.
However, since the film carrier is generally stored in the form of a roll wound on a spool or reel, it has a tendency to curl up when unwound from the reel. Due to the curling tendency of the film carrier, the outer leads formed by stamping from the same film carrier are necessarily curved or otherwise deformed to some extent.
On the other hand, a process for bonding semiconductor chips to a film carrier is generally known as "inner bonding". In the inner bonding, inner leads on the film carrier are attached by thermocompression bonding to an electrode portion formed on a surface of each semiconductor chip. During the thermocompression bonding, the inner leads are liable to thermal deformation.
For the reasons described above, in the outer lead bonding of semiconductor devices using a film carrier, deformation of the outer leads is inevitable. As a consequence of the deformation, the outer leads must be observed by a camera, for example, in order to detect the arrangement and position of the outer leads accurately before the semiconductor device is mounted on a substrate.
FIG. 6 illustrates a conventional electronic component observation system which includes a transfer head 26 mounted on an X-Y table 29 composed of an X-table 29a and a Y-table 29b. The X-table 29a and the Y-table 29b are movable in horizontal planes in the directions perpendicular to each other. A vacuum nozzle 27 extends vertically from a lower end of the transfer head 26 and has, at its lower end, a suction hole communicating with a vacuum source such as a suction pump (not shown). A semiconductor device P is held by the vacuum nozzle 27 at a position directly above a camera 6. In this condition, the outer leads L of the electronic component P are observed by the camera 6 and the arrangement and position of the outer leads L are detected.
Due to the curing tendency of a base film carrier, the outer leads L are generally curved or otherwise deformed to some extent ad described above, so that an accurate detection of the arrangement and position of the outer leads are substantially impossible. Accordingly, if the electronic component P were mounted on a substrate 101 carried on a table 103 based on the result of such inaccurate observation, misalignment or mismatching between the outer leads L and electrodes 102 on the substrate 101 would result.